The present invention relates to a triggering element for a portable heat pack, more particularly, a trigger element which generates an oscillation wave initiate a crystallization heat contained in a sealed bag.
Referring to FIG. 1, a conventional portable chemical bag warmer comprises a sodium acetate solution 3, which generates a crystallization heat, contained in a sealed bag 1. A trigger is typically formed in a thin disc-shape made of a metal piece and placed in the inside of the sealed bag in a non-fixed manner. The trigger has a plurality of slits which initiate an oscillation wave when the edges that form the slits make contact creating friction.
The liquid sodium acetate solution 3 is initiated to start crystallization to generate heat when triggering member is pressed down and up causing edges of the slits 7 to make contact creating a friction, thereby an oscillation wave is generated. However, if the initial triggering action fails to create the oscillation wave, then the user must repeat the pressing process in attempt to generate the oscillation wave which is inconvenient for the user to operate.
U.S. Pat. No. 5,205,278 utilizes a disc-shaped element made of a flexible metal with a center portion divided into four sectors to direct the vibration to four directions as a trigging member. However, since the surface of the trigging member dose not automatically restore back to the original shape and if the oscillation wave is not generated in the first attempt, the user must manually return the trigging member to the original state in order to make a second attempt to generate the oscillation wave.
Still, U.S. Pat. Nos. 4,899,727 and 4,572,158 disclose triggering members having different formation of the slits and the edges that form the slits in effort improve the reaction effect in initiating crystallization of the sodium acetate solution. However, both inventions failed to provide the triggering member which automatically returns to the original configuration after a snap-action causing the trigger member to deform.